The present invention relates to a hydraulic control system for an internal combustion engine, which has two hydraulic operating mechanisms operated independently by oil pressure of a common oil pressure source. The present invention further relates to a hydraulic control system for an internal combustion engine, which has two variable valve timing control mechanisms capable of varying lift characteristics of at least one of an intake valve and an exhaust valve.
In the field of internal combustion engines, it is a common practice to actuate various kinds of hydraulic operating mechanisms by using an oil pump for circulation of lubrication oil as an oil pressure source. Examples of such hydraulic operating mechanism are a variable valve timing control mechanism for varying the opening and closing timings and the lift of the intake and exhaust valves in accordance with the operating condition of the engine and a variable compression ratio control mechanism for varying the piston stroke of each cylinder and thereby varying the compression ratio in accordance with the operation condition of the engine.
An example of a hydraulic variable valve timing control mechanism is disclosed in Japanese Patent Provisional Publication No. 5-248217. This variable valve timing control mechanism is capable of varying the opening and closing timings of the intake and exhaust valves in two steps by switching from one of a low-speed rocker arm and a high-speed rocker arm to another. Other variable valve timing control mechanisms are a variable phase control mechanism for varying the operation angle phase (i.e., maxim lift phase) of the intake and exhaust valves, an operation angle varying mechanism for varying the operation angles and valve lifts of the intake and exhaust valves and a valve stop mechanism for temporarily stopping the intake and exhaust valves of some of the cylinders.
In this connection, in case two hydraulic operating mechanisms which are operated independently by oil pressure of a common oil pressure source e used in an internal combustion engine, there is a possibility of causing the following problems. Namely, In case the operating conditions of both of the hydraulic operating mechanisms are changed simultaneously, particularly at a low-speed engine operating condition where the oil pressure produced by the oil pump is low, there is a possibility that the hydraulic operating mechanisms become poor in responsiveness due to a lack of the oil pressure supplied thereto. To prevent such deterioration of the responsiveness, it is considered to use an oil pump, accumulator or the like for the hydraulic operating mechanisms"" exclusive use. However, in this instance, a hydraulic circuit of the hydraulic control system becomes complicated in structure, thus causing a possibility of increasing the weight and the cost.
Particularly, in case the two hydraulic operating mechanisms are variable valve timing control mechanisms for varying the lift characteristics of the intake and exhaust valves, it is highly necessitated to change the operating conditions of the variable valve timing control mechanisms at the same timing so as to attain the required lifts which vary largely in accordance with the operating conditions of the engine at idling or at full-throttle operation.
For example, in case a variable phase control mechanism for varying the operation angle phase of an intake valve and a valve stop mechanism for temporarily stopping the intake and exhaust valves of some of the cylinders are used, it is desirable, when the valve stop mechanism is operated to stop the intake and exhaust valves of some of the cylinders, to advance the operation angle phase of the intake valve by the variable phase control mechanism so that a predetermined torque can be attained by the remaining cylinders. In this instance, the delay of the responsiveness of the valve stop mechanism becomes a particularly large problem. Namely, in the cylinders where the intake and exhaust valves are stopped, it is necessitated to inhibit injection of fuel. If there is a difference between the period during which the intake and exhaust valves are actually stopped and the period during which injection of fuel is actually inhibited, it is possible that fuel is injected during the time of the valves being stopped. This is particularly not desirable.
It is accordingly an object of the present invention to provide a hydraulic control system for an internal combustion engine, which has two hydraulic operating mechanisms operated independently by oil pressure of a common oil pressure source and which is simple in structure and has an improved responsiveness.
To accomplish the above object, there is provided according to an aspect of the present invention a hydraulic control system for an internal combustion engine comprising a first hydraulic operating mechanism, a second hydraulic operating mechanism, the first hydraulic operating mechanism and the second hydraulic operating mechanism being operated independently by oil pressure of a common oil pressure source, and a circulation line that supplies pressure oil discharged from the first hydraulic operating mechanism to the second hydraulic operating mechanism.
According to another aspect of the present invention, there is provided a hydraulic control system for an internal combustion engine comprising an oil pressure source, an oil sump, a first hydraulic operating mechanism, a second hydraulic operating mechanism, a first hydraulic control valve for selectively communicating the first hydraulic operating mechanism with one of the oil pressure source and the oil sump thereby controlling an operation of the first hydraulic operating mechanism, a second hydraulic control valve for selectively communicating the second hydraulic operating mechanism with one of the oil pressure source and the oil sump, a control line fluidly connecting between the second hydraulic control valve and the second hydraulic operating mechanism for conducting pressure oil supplied to and discharged from the second hydraulic operating mechanism, and a circulation line connecting between the first hydraulic control valve and the control line for supplying pressure oil discharged from the first hydraulic operating mechanism to the second hydraulic operating mechanism.
According to a further aspect of the present invention, there is provided a hydraulic control system for an internal combustion engine comprising a phase control mechanism for varying a phase of an intake valve, a valve stop mechanism for temporarily stopping intake and exhaust valves of some of cylinders, the phase control mechanism and the valve stop mechanism being operated by oil pressure of a common oil pressure source, and means for supplying pressure oil discharged from the phase control mechanism to the valve stop mechanism in addition to pressure oil supplied from the oil pressure source to the valve stop mechanism when the phase of the intake valve is advanced by the phase control mechanism and the intake and exhaust valves of some of the cylinders are stopped by the valve stop mechanism.